1. Field of the Invention
The present invention relates to image forming apparatuses, such as copiers and printers, which can be used in areas where different supply voltages are used, and to power supply devices which are suitable for being installed in the image forming apparatuses.
2. Description of the Related Art
Image forming apparatuses have power supply devices that convert voltages of a commercial alternating-current power supply (hereinafter, simply referred to as an AC power supply) into direct-current (DC) voltages. Different AC power supply voltages are used in different countries. AC power supply voltages are broadly classified into two systems: the 100 V system, such as 100 V or 120 V, which is used in Japan and North America, for example; and the 200 V system, such as 220 V or 240 V, which is used in Europe, for example. When AC power supply voltages having a large difference therebetween are used, conversion efficiencies, current ratings of components, and temperatures are required to satisfy the broad range of AC power supply voltages, resulting in difficulty in designing the configuration of an apparatus. Accordingly, two types of power supply devices are typically provided which have different configurations, each of which is optimized for a corresponding one of the 100 V system and the 200 V system.
However, since two types of power supply devices for the 100 V system and the 200 V system need to be provided, it is difficult to manage the production and inventories of the power supply devices. If a power supply device is compatible with both of the 100 V system and the 200 V system (hereinafter, such a power supply is referred to as a universal power supply device), only one type of power supply device is needed, achieving simplified management. A universal power supply has a configuration that has been optimized in accordance with the output voltage and output power. There is a method in which, when output power is small, the current ratings of components of a power supply for the 200 V system are increased so that the power supply is compatible with the 100 V system. Such a power supply employing this method is called a full-range power supply. In addition, Japanese Patent Laid-Open No. 2000-316280 describes a power supply that has a configuration in which a rectifier circuit outputs a voltage of the 200 V system regardless of the AC power supply voltage by changing the circuit configuration of the power supply. In this power supply, when an AC power supply voltage of the 100 V system is supplied, the circuit configuration is changed to perform voltage-doubler rectification to generate a voltage which is double the AC power supply voltage. When an AC power supply voltage of the 200 V system is supplied, the circuit configuration is changed to perform full-wave rectification to generate a voltage which is the same as the AC power supply voltage. Furthermore, this power supply includes a voltage detection circuit for detecting the voltage of the AC power supply, and is automatically switched to perform voltage-doubler rectification or full-wave rectification in accordance with the detected voltage.
A typical image forming apparatus has multiple power supplies because the image forming apparatus needs multiple voltages. Similarly, a universal power supply device has multiple universal power supplies having the above-described configurations.
To satisfy a recent demand for reducing power consumption, the following operations have been needed. A power saving mode is provided in an image forming apparatus. The image forming apparatus determines whether each of the circuits in the image forming apparatus needs to operate in the power saving mode or not, and turns off the circuits that do not need to operate in the power saving mode. To perform the above operations, the image forming apparatus needs to have a configuration in which the image forming apparatus individually turns the circuits on/off. Similarly, the universal power supply device desirably has a configuration in which power supplies that do not need to operate in the power saving mode can be stopped to achieve reduction in power consumption.